The invention relates to electrical generators and motors, and more particularly, to transformers used in portable electrical generators and motors.
A reliable power source is required in innumerable situations where conventional power supplies are inaccessible. This is commonly the case with respect to recreational vehicles and other outdoor activities. For example, a wide range of electrical equipment and appliances, such as light sources, power tools, and vehicles, are commonly used in places where access to conventional electrical outlets is inconvenient or impossible. Running electrical extension cords from an outlet within a building to the roof of the building or outside to an electrical tool consumes valuable time.
There are two practical options for supplying power at a remote location: a battery or a portable generator. Batteries have a finite lifetime, and are prone to failure at the worst possible times and places. In particular, failure of a vehicle, boat, or aircraft battery may leave the user stranded in a frustrating or even dangerous situation. Consequently, portable generators are often more appropriate.
Portable generators commonly comprise a conventional diesel or gasoline powered engine which turns a crankshaft. The crankshaft transfers power to a conventional generator, such as a rotor for a conventional induction generator. The rotor generates a magnetic field, which rotates concomitantly with the rotation of the rotor and crankshaft. As the magnetic field intercepts the windings on the stator, electrical current begins to flow. That current is used to supply power to the equipment or appliance. Alternatively, a magnetic field may be created by current flowing through the stator winding, and as the rotor rotates through the magnetic field, current is generated in the rotor windings, which may be used to supply power to a tool or appliance.
Generators commonly include brushes and slip rings to transfer electrical current to and from the rotating part of the generator. Slip rings are typically circular conductors connected to the respective terminals of the rotating windings. Brushes represent stationary electrical terminals constantly in contact with the slip rings as they rotate, so that a conductive path is established between the rotating rings and the brushes and hence between the generator terminals and the rotating windings. Although slip rings and brushes provide effective electrical transfer, they are subject to wear and failure. As a result, generators equipped with brushes are typically unsuitable for remote or emergency uses.
Brushless designs are well known in the field of generator and motor design. Most brushless designs, however, add significant weight and length to the generator. For example, one common design requires a secondary alternator having a rotor which is also rotated by the crankshaft. In the secondary alternator, current flowing in the stator winding generates a magnetic field through which windings on the secondary alternator's rotor pass. Current induced in the secondary alternator's rotor winding supplies current to the field winding on the rotor of the primary generator, which then rotates to generate the main current in the stator winding. Because the secondary alternator's winding is rotating with the primary generator's field winding, the need for brushes and slip rings is eliminated. The secondary alternator, however, adds substantial weight and length to the generator. As a result, the generator is unwieldy and bulky, reducing its portability. For some applications requiring compact generators, such as recreational and emergency vehicles, a large generator may consume space that is preferably devoted to other equipment.
Smaller, more portable generators, on the other hand, are unable to supply sufficient power over a reasonable duration of time. Such relatively small portable generators commonly provide relatively low power, unsuitable for supplying multiple lights, appliances, or equipment that draw significant power.